|
How to Identify PearlsWhat is the most important characteristic in how to identify pearls? How to identify pearls...chemical composition.Chemically considered, aside from the nucleus, the structure of pearls is identical in composition with that of the nacre of the shell in which they are formed. Analysis has shown that those from the fresh-water mussels of England and Scotland and from the pearl-oysters of Australia and of Ceylon, have nearly identical composition in the proportion of about 5.94% of organic matter, 2.34% of water, and 91.72% of carbonate of lime. The specific gravity ranges from nearly 2 to about 2.75, increasing with the deposit of the nacreous coatings. How to identify pearls...lusterThe distinctive characteristic, the great beauty of a true pearl, is its luster or orient, which is the subdued iridescence, rather than the glittering brilliance of the diamond; and unless the shelly growth be lustrous it does not rank as a gem pearl, no matter how perfect its form or beautiful its color. This luster is due to the structural arrangement of the surface as well as to the quality of the material. The nacreous material forming true pearls, and likewise mother-of-pearl, is commonly deposited in irregular tenuous layers, very thin and very small in area compared with the surface of the pearl. The laminae overlap one another, the surfaces are microscopically crumpled and corrugated and the edges form serrated outlines. The greater the angle which the laminae form with the surface, the closer will be these serrated outlines, and where the plane of the exterior lamina is parallel with the plane of the surface the lines are not present. This arrangement causes the waves of light to be reflected from different levels on the surface, just as in a soap bubble, and the minute prisms split the rays up into their colored constituents, producing the chromatic or iridescent effect. In the shells of some mollusks--as the edible oysters (Ostrea) or the giant clam (Tridacna),--there is almost a total absence of the crumpled corrugated laminae, and, consequently, there is little luster. In others the nacre is of better quality, resulting in superior orient, and it probably reaches its highest degree of perfection in the pearl-oyster (Margaritifera). The position of the pearl within the shell may greatly affect the quality of the material and, the orient. The choicest are commonly found within the soft parts of the animal, and those of poorer quality are at the edges of the mantle, or within the fibers of the abductor muscle of bivalves. How to identify pearls...structureThe structure of pearls may be studied by examining thin cross sections under the microscope, or by transmitted polarized light. It appears that ordinarily a pearl is made up of many independent laminae superimposed one upon another "like the layers of an onion". When subjected to sufficient heat, the laminae separate from each other, as do shells of edible oysters and similar mollusks. How to identify pearls...formPearls assume as almost infinite variety of forms, due largely to the shapes of the nuclei, and also to their positions within the mollusk. The most usual--and also the most valuable--is the spherical, resulting from a very minute or a round body as a nucleus and the uniform addition of nacre on all sides. Of course, spherical pearls can result only where they are quite free from other hard substances; consequently they originate only in the soft parts of the mollusk and not by the fixation of some nucleus to the interior surface of the shell. The perfectly spherical pearls range in weight from a small fraction of a grain to three hundred grains or more, but it is very, very rare that one of choice luster weighs more than one hundred grains. The very large ones, weighing in excess of one hundred grains, are called "paragons". The small pearls--weighing less than half a grain each--are known as "seed-pearls". The very small ones, weighing less than 1/25 of a grain, are called "dust-pearls". These are too small to be of economic value as ornaments. How to identify pearls...various formsSlight departures from the perfect sphere result in egg shapes, pear shapes, drop shapes, baroque, button shapes, etc. Some of these are valued quite as highly at the present time as the spherical pearls, and many of the most highly prized pearls in the world are of other than spherical form. Indeed, pearls of this kind are found of larger size than the perfectly round pearls. For example, the egg-shaped pear, called "la Regente," weighs 337 grains. In the American Unios there is a strong tendency to produce elongated pearls near the hinge of the shell, which are known as "hinge pearls". There are several standard forms of these hinge pearls. Many are elongated or dog-toothed, some are hammer-shaped, others resemble the wings of birds, the petals of flowers, the bodies of fish, and various other objects. How to identify pearls...baroque examplesSome irregular pearls or baroques are very large, weighing an ounce or more. A well-known example is the Hope Pearl, which weighs three ounces. Some remarkable examples of baroque mountings in fanciful forms such as horses, hippocampi, lambs, dragons, etc., have been produced, and a few are to be found in most of the large pearl collections, such as in the British Museum collection.  Dragon Pearl British Museum Photo: Kari How to identify pearls...colorThe color of pearls has no connection with the luster. In general it is the same as that of the shell in which they are formed. Black pearls are found in the black shells of Mexico, and pink pearls in the pink-hues Strombus of the Bahamas. Ceylon pearls are seldom of any other color than white, and Sharks Bays are almost invariably quite yellow or straw-colored, while those of Venezuela are commonly yellowish tinged. But from other localities, pearls simulate every tint of the rainbow, as well as white and black. The most common, as well as the most desirable ordinarily, is white, or rather, silvery or moonlight glint, but yellow, pink, and black are numerous. They may also be piebald--a portion white and the rest pink or brown or black. The pearls from Mexico, the South Sea Islands, and the American rivers are especially noted fro their great variety of coloration, covering every known tint and shade. Information on how to identify pearls from Kunz and Stevenson as found in their book about pearls, 1908. Homepage for Karipearls
|
